I was frightened of vaccines back when I was pregnant with my daughter 12 years ago.

I lived in the San Francisco bay area at the time, and if you’ve ever lived in the Bay Area, you know there are ways of thinking there that aren’t questioned like they would be elsewhere — especially those related to motherhood and children. The home-birth collective I was part of held an “immunization panel,” inviting parents to ask questions of practitioners on both sides of the debate. When I look back on it, I’m not sure how much range of perspective the panel included. But I really thought I had done my homework on vaccination. I read everything I could get my hands on, talked about it with our midwives, discussed it with fellow pregnant friends. And I came to believe that my daughter’s immune system should have a chance to build up on its own, without being bombarded with viruses and chemicals.

Before she was born, I spoke with her pediatrician about a delayed and partial vaccine schedule. And that is what we followed. For her first year of life, my daughter wasn’t vaccinated. I breast-fed her to help strengthen her immunity. I kept her out of day care so she wouldn’t be exposed to all of those germs. I steered her away from anyone coughing at the grocery store. I believed that I could keep her safe.

And when she turned 1, a magical number I’d decided was when her immune system would be strong enough, I took her to get her first shot. On her immunization record, it says that shot was for Hib, which prevents meningitis and pneumonia, among other diseases. A month later she got her first polio shot, and five months after that she got her first dose of DTaP, except I asked for the version that did not contain the P for pertussis. My understanding was that she was past the point when whooping cough could shut down her airways; I was more terrified of what I’d heard was in that part of the vaccine and how it could permanently damage her body. I can’t remember anymore what scared me so.

My attitude toward vaccines began to shift when I got sick with shingles and my then-3-year-old daughter kept wanting to touch the fiery blisters on my arm, chest and back. She could get chickenpox from those blisters, and I couldn’t imagine caring for a sick child while I myself was so miserable. So I took a cab across Jerusalem, where we were living, picked up a dose of chickenpox vaccine and took my daughter to an American doctor to administer it. He warned that it would take two weeks to build up her immunity and that she would need a second dose at some point for the vaccine to be even more effective. I felt some disappointment that I wasn’t holding out for her to get chickenpox naturally, but I was also relieved.

We left our life abroad abruptly and unexpectedly three months later, when we learned that our second daughter, who had been growing inside me for 21 weeks, had a life-threatening congenital defect. Our baby girl was born back in the Bay Area and was immediately hooked up to machines that helped her breathe and tubes that administered medicine and fed her my breast milk. Hoping for her survival, I approached the doctors with questions about vaccines. I was concerned about protecting my fragile daughter from viruses such as pneumonia that could kill her, but I also worried about harming her with more medicine than she could handle. The doctors explained that her well-being would need to be assessed day by day, sometimes hour by hour, and that it would be clear when she was ready to be vaccinated. Ultimately, none of it mattered. After 58 days in the NICU, I held my daughter as she took her last breaths and her spirit let go of her body.

After our baby died, we moved to the Midwest, and our new pediatrician was a heavy pusher of vaccination. “You can go blind from measles,” she explained. At first it irritated me, and I clung to my beliefs about not wanting to bombard my healthy 5-year-old with preservative-packed shots, many targeting diseases that didn’t even exist anymore, at least not in the United States.

But I realized I could no longer explain to the pediatrician or to other moms why vaccines were so dangerous. My fear of immunizations was dissolving, and I no longer felt the way I had when my first daughter was born.

When we made our decisions about vaccines the first time, it was all abstract. My child couldn’t die from measles, I told myself. My mom had had measles, and she was just fine. I hadn’t yet spent those weeks in the NICU, praying over my child that the fluid in her lungs wouldn’t become full-blown pneumonia. I hadn’t seen all of the other sick babies around her. I hadn’t heard from other bereaved parents about all the ways babies can die.

After all that, I could no longer take my child’s health — or my ability to protect it — for granted. And so I gradually let myself trust our new pediatrician and the vaccines she encouraged. My only holdout was the flu shot. I still believed that for my healthy daughter, and for our healthy family, the flu wasn’t a danger. We all took our vitamin D and fish oil, and ate well and washed our hands. The viruses our daughter got about once a year, whether the flu or something else, meant a lot of movies while she lay on the couch drinking Gatorade and sucking on popsicles; those viruses would strengthen her body to protect her from worse things.

It wasn’t until I read Eula Biss’s January 2013 essay on vaccinations in Harper’s magazine that I understood, for the first time, how herd immunity works. “Any given vaccine can fail to produce immunity in an individual, and some vaccines, like the influenza vaccine, often fail to produce immunity,” Biss wrote. “But when enough people are given even a relatively ineffective vaccine, viruses have trouble moving from host to host and cease to spread, sparing both the unvaccinated and those in whom vaccination has not produced immunity.”

I was reminded of a voice — my own voice from years before, when my first daughter was a baby — saying, “She’s safe even without her shots because everyone around her is vaccinated.” I actually said that, several times, to several people. Friends said the same thing to me about their unvaccinated children. We had that luxury — we could count on herd immunity to protect our children.

I can’t say exactly why the idea of protecting others hadn’t hit me before — I have always considered myself a sensitive and empathetic person. But I hadn’t thought about old people, those who could die even from the flu. I hadn’t thought about pregnant women and their babies. I hadn’t thought about children like my second daughter, who are too sick to be vaccinated but who need more than anyone to be protected from illness.

My son came to us through adoption, and there is so much we don’t know about his biological family’s health history. He is almost 2 years old, and he has had almost all of his shots according to schedule. The only one I requested delaying, because he was born early and weighed less than four pounds, is Hep B, but he had that shot within his first year.

My daughter is all caught up on her shots, too — after many doctors’ visits and trips for frozen yogurt afterward. At her annual physical this past week, she got some of her boosters and one vaccine that didn’t exist when I was her age: HPV. A vaccine that can help prevent the only known cause of cervical cancer? To me, that one is a no-brainer.

And this year we all got flu shots, including my strong-as-an-ox husband, because his work takes him to hospitals, nursing homes and other places where people are vulnerable.

I am not naive about this. I still read medical journal articles and philosophical pieces about vaccination, and I ask a lot of questions.

But I have accepted that I can’t protect my family from everything that is out there (and everything that is already a part of us). All I can do is my best to nurture our perfectly imperfect bodies.